University of Illinois Urbana-Champaign

Lewis base catalyzed enantioselective sulfenoamination of alkenes

Chi, Hyungmin

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CHI-DISSERTATION-2016.pdf

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https://hdl.handle.net/2142/95503

Description

Title
Lewis base catalyzed enantioselective sulfenoamination of alkenes
Author(s)
Chi, Hyungmin
Issue Date
2016-12-02
Director of Research (if dissertation) or Advisor (if thesis)
Denmark, Scott E.
Doctoral Committee Chair(s)
Denmark, Scott E.
Committee Member(s)
  • Burke, Martin D.
  • van der Donk, Wilfred A.
  • Rauchfuss, Thomas B.
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Date of Ingest
2017-03-01T16:37:04Z
Keyword(s)
  • Sulfenoamination
  • Enantioselective catalysis
  • Lewis base
  • Negative catalysis
Abstract
The concept of Lewis base activation of Lewis acid has been successfully applied to the enantioselective sulfenoamination of olefins. The unreactive, achiral Lewis acidic sulfenylating agent, N-arylthiophthalimide, is activated by the coordination of a chiral Lewis base, binaphthyl-derived selenophosphoramide, in presence of a Brønsted acid as a co-catalyst. The Lewis base-acid adduct exhibits a strong sulfenylating ability towards various olefins with formation of enantioenriched thiiranium ion intermediates. These configurationally stable thiiranium ions are stereospecifically captured by amines and anilines to afford nitrogen-containing heterocycles, such as piperidines, azepanes, and tetrahydroquinolines. In the course of developing an enantioselective carbosulfenylation of alkenes, a seemingly contradicting phenomenon of a catalyst inhibiting a stoichiometric reaction was observed. In the absence of catalyst, the background reaction rates were comparable to or greater than the catalyzed process, despite the observation of highly enantioenriched product when a chiral, nonracemic catalyst was employed. Detailed kinetic and spectroscopic studies revealed that the conversion of the Lewis base pre-catalyst to the catalytically active species was responsible for the observed comparable reactivity. Specifically, the equimolar formation of the byproducts of the catalyst activation, sulfonate ion and phthalimide, buffered the Brønsted acid, resulting in inhibition of the uncatalyzed racemic pathway. Therefore, the operating background reaction under catalytic conditions cannot be represented by simply omitting the catalyst.
Graduation Semester
2016-12
Type of Resource
text
Permalink
http://hdl.handle.net/2142/95503
Copyright and License Information
Copyright 2016 Hyungmin Chi

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